1. Field of the Invention
This invention relates to a Tb- or Eu-containing fluorophosphate fluorescent glass capable of converting invisible ultraviolet rays into visually observable visible rays with a high efficiency and available for controlling the optical axis of a laser beam such as excimer laser, etc.
2. Description of the Prior Art
Phosphors using rare earth elements have widely been used up to the present time, mainly, as phosphors for lamps, color picture tubes, etc. Of late, materials for the anti-Stokes-wise wavelength conversion of infrared light into visible light have extensively been studied, for example, as to application to laser materials.
Tb ion showing the strongest fluorescence (green) in the visible region, among the rare earth element ions, has been put to practical use as intensifying screens, projection cathode-ray tubes, high color rendering fluorescent lamps, etc. Eu ion showing a fluorescence with a narrow spctrum width in the red region has been put to practice as color picture tubes, high color rendering fluorescent lamps, etc. As described above, a phosphor using Tb or Eu has already been put to practical use, but such a phosphor is an opaque material which is obtained by coating a suitable carrier with a powdered phosphor to thus give only a superficial emission.
As such a glass utilizing fluorescence of Tb or Eu, there are used those described in Japanese Patent Publication Nos. 27047/1982 and 27048/1982.
However, the glasses described in these publications, for example, in Japanese Patent Publication No. 27047/1982 contain only at most 1.5 mol % of Eu.sub.2 O.sub.3 as a fluorescent agent. In the case of Japanese Patent Publication No. 27048/1982, only at most 1.5 mol % of Tb.sub.2 O.sub.3 is contained as a fluorescent agent and other rare earth elements such as Eu.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Sm.sub.2 O.sub.3, Tm.sub.2 O.sub.3, etc. are simultaneously added for imparting multi-coloring property.
When some varieties of fluorescent agents are present in admixture, in general, the fluorescent intensity is decreased by their interaction and a high efficiency emission cannot be obatined.